Oscillator gets dirty as keys go higher (sinus)

[superplek]

Hi there, there's a little problem I need to wrap my head around. If I, in my VST, just output what's supposed to be, I see (using a scope) the phase shifting unless I use an A note in any octave.

Now my domain is [0..1] and I do have that darned loop everyone has where I have a pitch and I keep adding it to the phase until I overshoot and then subtract 1 and go my merry way. This could of course have something to do with it.

So, I'm questioning: is what I am seeing natural (since I tried high keys on the DX7 and the Reface CP and they seem to suffer the same artifact @ very high pitched notes) or am I doing something fundamentally wrong here? I hope it's the latter.

Thanks,
- Niels

[njdewit]

Figured what it is. Purely a matter of a signal not aligning with a discretized rational intervals, which in turn causes slight phase shifts (extra sideband impulses).